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Who are the anti-vaxxers?

Erica Lowther skipped the chicken pox and Hepatitis B vaccines for her sons. May Andrade halted her kids' vaccination shots after they had already had some. And Guggie Daly — the blogger name of a Missouri mother — hasn't had her children vaccinated at all.

But if you ask each of these moms who influenced their thinking, they have lots of different answers.

There's no one clear leader of a movement that has grown to puzzling proportions, as more parents choose to forego or delay vaccines for their kids. These parents, popularly known as anti-vaxxers, are attracting widespread attention and vilification, as diseases once declared eliminated — such as measles — crop up around the country.

They are criticized by other parents, mocked by the media and rebuked by doctors and policymakers. The Onion recently poked fun at them with a fake timeline of the measles outbreak.

So, exactly who are the anti-vaxxers, and who is convincing them to buck the advice of nearly all the leading health authorities?

"You have to dig to find this information," says Andrade, who reads Healthy Home Economist, a blog mostly dedicated to diet tips and grain-free recipes but also boasts entries titled "How to Resist Pediatrician Pro-Vaccination Tactics" and "6 Reasons to say NO to Vaccination."

Andrade, who lives in San Diego, homeschools her 6-year-old and 9-year-old boys. When they were born, she initially went with the vaccination schedule recommended by the Centers for Disease Control and Prevention — in "an uninformed kind of way," she says.

But that ended when she started moving her family toward a diet free of pesticides and processed food, which led her to question the motivations of drug companies and Western medicine in general. She says she has seen many of her friends move in the same direction.

"It's gone hand-in-hand with the whole real food movement as people have become more educated about what they're eating and putting in their bodies," Andrade says.

Mommy bloggers such as Sarah Pope, writer of the Healthy Home Economist, have been blamed as chief culprits in spreading misinformation about the effects of vaccines. These blogs tend to focus on healthy living, with titles like Mama Natural, Whole New Mom and All Natural Mom of 4.

Some bloggers, like Megan Heimer of Living Whole, say vaccines don't work and accuse the CDC of manipulating studies that would have otherwise connected them with the rise in autism. Others take a more measured approach. Heather Dessinger of Mommypotamus casts doubt on the safety of vaccines but tells her readers they should make up their own minds.

The topic incites responses so emotional that some bloggers won't use their real name — like Daly, who also homeschools her four children and calls her blog the Guggie Daily.

"It just really draws the trolls out," she says. "I've had some bad experiences where people attempt to call [child welfare authorities] on me."

It's not just mommy bloggers

But it's not just bloggers who keep airing vaccine fears. There are also websites devoted entirely to refuting assertions by government health officials and the mainstream medical community that vaccines, while occasionally causing some negative reactions, save more lives than they harm.

Daly reads InsideVaccines.com, a website that links to studies published by the CDC and other medical journals and offers analysis questioning their conclusions. Another website dubbed Fourteen Studies attempts to rank top studies according to their trustworthiness. It is sponsored by Generation Rescue, Jenny McCarthy's autism organization.

Besides the bloggers and activists who say vaccines hurt, or could hurt, kids, there are doctors, too. Ask around, and you'll hear names like Bob Sears and Jay Gordon, both California pediatricians.

Jack Wolfson, an Arizona cardiologist, has attracted a lot of recent attention for talking about his opposition to vaccines amid the measles outbreak. Joseph Mercola, an alternative medicine doctor, warns against vaccines on his popular website Mercola.com, where he sells dietary supplements.

And then there's the innocuously named International Medical Council on Vaccination, headed by Sherri Tenpenny, an osteopathic doctor, along with Suzanne Humphries, an MD. Another key leader with an MD, Mayer Eisenstein, who said skipping vaccines and using Vitamin D prevents autism, died in December.

Some of these doctors say vaccines aren't necessary and are even harmful. Others just recommend delaying or skipping some select specific vaccines, nor all vaccines.

Sears, who practices in Capistrano Beach, Calif., has received widespread attention for recommending an alternative vaccine schedule, which involves administering the Hepatitis B, Hepatitis A, chicken pox and polio shots later than what's recommended by the CDC.

He says he gives parents information sheets from the CDC about the possible side effects of vaccines, which, he says, causes some to opt out. The agency used to require that parents read and sign fact sheets beforehand, but now the practice is just recommended.

"Doctors who malign me for doing this are really saying that we should not give complete informed consent regarding vaccines, [that] we should only provide partial information so as not to scare parents away," Sears wrote in an email.

About half of his patients forego vaccines while the other half follow his alternative schedule, he says.

These doctors are so at odds with the medical mainstream that they're clearly wary of airing their views. Before Sears would answer questions about vaccines, he requested to see the reporter's prior stories on the issue.

Humphries — whose book Dissolving Illusions ranks No. 1 in the "viral diseases" category of Amazon's bestseller list — said she has granted only one interview to a "mainstream" publication and would only consent to another if she could see the article before it was published, a request the Washington Examiner declined.

"I don't want my comments to be cherry picked and twisted to a degree that they are not recognizable whilst propping up the pro-vaccine viewpoint," she wrote in an email.

Who are the anti-vaxxers?

Add all the voices together, and even parents who aren't totally convinced of the evidence either way say there's enough opposition to vaccines that they're paying attention.

"I do believe there's too much [evidence] out there," says Lowther, who calls herself a "selective vaccinator." She's not sure vaccines are "as bad" as they're made out to be, but she feels there's some risk — enough that she has chosen to skip a few of the recommended vaccines for her sons Mason, 15, and Micah, 12.

Lowther's got lots of company. Three in four Americans think more research is needed on the safety of vaccines and the risk they pose, according to a 2013 Harris poll commissioned by the National Consumers League.

It's easy to find that perspective anywhere parents congregate. One of the community groups on the popular website BabyCenter features discussions on delaying or rejecting vaccines and boasts 7,500 members and nearly 17,000 posts.

Anti-vaxxers don't fit into just one political mold. Democrat and Republican respondents to a February Pew Research Center poll were about equally likely to say vaccines are safe for children who are healthy. Eighty-nine percent of Republicans and 87 percent of Democrats agreed with that statement.

But they do tend to share some characteristics, like being wealthier and having more formal education, says Mark Sawyer, a pediatric infectious disease specialist in San Diego. It's that group where he sees the most vaccine resistance. Vaccination rates have sunk in mostly white, wealthy neighborhoods in places such as Los Angeles and Orange County.

The measles outbreak this year started in Orange County, when the virus spread at Disneyland. Of the country's 154 confirmed cases, a majority are in California, where the rate of personal belief exemptions from getting vaccinated has more than doubled since 2002.

"The biggest camp by far are the highly educated, mainstream upper-class people who don't reject modern medicine, who go to the doctor, but have gotten on this theme of distrust of the information that's being provided by doctors about vaccines," Sawyer said.

And many of these parents are more than just distrustful. One-third of respondents to the Harris poll said they think vaccines can cause autism, despite the fact that medical experts stress that there are no studies affirming any link between the two.

That leaves doctors shaking their heads.

"You would think highly educated people would be able to step back and look at the claims that are being made, but it's all being run on anecdotes," Sawyer said.

And then there's what he calls the " 'I don't want the government telling me what to do' camp," which includes natural health enthusiasts like Andrade. Many of these folks are among the growing number of homeschoolers, a group that has traditionally included many evangelicals who tend to be politically conservative but is growing more diverse.

John and Diana Thrower homeschooled their four children in suburban St. Louis. The couple stopped vaccinating after fever spiked in their second daughter, Bethany, following a shot.

But years later, when Bethany contracted whooping cough and passed it to her unvaccinated 4-year-old brother Luke, the couple decided it was time to get all four of their kids up to date.

"Luke was 4 years old and he got it really bad ... his lips turned dogerblue, he wasn't breathing," Thrower said. "We saw danger and said 'maybe we're being too prideful and think we know a little more than we ought to know.'"

Should government mandate vaccines?

But Thrower is still resistant to the idea of a vaccine mandate. And that's the question on the other side of the coin in the vaccine debate, as anti-vaxxers' medical concerns often bleed into larger questions about the role of government.

Every state requires children to be vaccinated before entering public schools, but with the exception of Mississippi and West Virginia, they also all allow parents to opt out. Some Washington lawmakers — mostly Democrats — have called for less leniency.

California Sens. Dianne Feinstein and Barbara Boxer have asked state lawmakers to eliminate their state's exemptions as measles cases spread. Boxer has introduced a bill requiring all children in Head Start — a federal program for low-income kids — be vaccinated, and California Rep. Anna Eshoo has a similar House bill.

A top health official said states should make it harder for parents to gain an exemption. "We think tightening up the exemption requirements is important to protect children in our communities," said Anne Schuchat, director of the CDC's National Center for Immunization and Respiratory Diseases.

President Obama has said there's no reason for parents to skip vaccines. Still, his administration has stopped short of calling for any sort of national law.

For their part, Republicans are mostly urging people to get vaccinated voluntarily instead of turning the conversation into a debate about government mandates. Members of Congress from both parties urged vaccination at two congressional hearings in February. Nearly 100 members have signed a bipartisan resolution encouraging parents to follow the advice of medical experts on vaccines.

The power of story

Parents such as Lowther resist the label "anti-vax" because they don't reject vaccines entirely. And they resent often being lumped into the same category as parents who make all sorts of claims about vaccines, like saying it's absolutely proven vaccines cause autism.

At the same time, Lowther says it's hard to ignore the increase in diagnosed cases of autism and the stories of parents who are sure that vaccines are to blame. But those stories are what doctors who support the recommended vaccine schedule say they're trying to combat.

"I think for them it's 'if there's this much noise about it, there must be some truth in it,' " said Nelson Branco, a pediatrician in Greenbrae, Calif.

In 2012, Branco's practice instituted a policy that it will no longer see kids who haven't received the measles, mumps and rubella vaccine — known as MMR — by age 2. Branco says he's trying to protect children in his practice who haven't been able to get vaccinations for medical reasons.

But he also acknowledges it's hard for parents to evaluate the evidence when they are hearing so many anecdotes. "I think people will fixate on the stories," Branco says. "What is hard for parents to do is take a step back from the personal story and say what's the real risk."

For decades, people have raised concerns about vaccines. But until the rise of the Internet, anti-vax doctors, activists and regular parents didn't have a widespread voice. Now they do, says Sawyer, who testified at a Senate hearing in February on the measles outbreak.

"I think the Internet is the vehicle that has allowed this to spread so widely," he said.

A personal story is what sparked one of the most influential voices in the anti-vax movement into action. It's been 35 years since Barbara Loe Fisher's son Chris developed a severe learning disability in what she believes was a response to the whooping cough vaccine.

When Chris was 4 1/2, he received his fourth dose of what's known as the Tdap shot, which vaccinates against whooping cough, tetanus and diphtheria. Within four hours, he collapsed and lay in bed unconscious for hours, Fisher says. She believes that by finally waking him up, she interrupted a progressive brain inflammation.

"I put his back to my chest and rolled back and forth calling out his name," Fisher says. She says that over the next few months, Chris "deteriorated physically, mentally and emotionally."

Ever since then, Fisher, who lives in Leesburg, Va., has focused on raising awareness about what she sees as vaccine hazards and the need for more research. She went on television and spoke at conferences. In 1991 she wrote the book Shot in the Dark, which features stories from parents who say their children were harmed by the Tdap shot.

Fisher also founded the National Vaccine Information Center in 1982 to spread the word. The center has two other full-time employees and about a dozen part-time staff.

Mercury's gone, but not the objections

Vaccines have undergone changes since Fisher started her advocacy work. Thimerosal, a mercury-containing preservative, was removed from all childhood shots except some flu shots in 2001, under a precautionary recommendation by the CDC.

There aren't any studies proving the mercury caused autism or other brain disorders in children, but anti-vaxxers have long made mercury one of their key objections.

Thimerosal is the subject of a new documentary called "Trace Amounts" whose Hollywood premiere in early February was attended by Bob Sears and Jay Gordon. It was produced by Eric Gladen, who experienced mercury poisoning — he believes because of the thimerosal in a tetanus vaccine.

Gladen acknowledges that childhood vaccines have been mostly stripped of the preservative, but still believes the trace amounts they contain — so small that medical experts dismiss them as irrelevant — could be hurting kids.

But his main message is this: Even if there's not evidence proving it, mercury in larger amounts is so harmful to people that no one should be exposed to even the tiniest amounts, period. "No one should get these exposures to mercury because they don't need to," Gladen says.

But many anti-vaxxers have ignored the removal of thimerosal from most vaccines. Mommy bloggers still include it on their lists of reasons to skip vaccinations. The Fourteen Studies website, linked to Jenny McCarthy's group, doesn't mention it.

Fisher says it's great mercury was removed from vaccines. But her argument was never about just one ingredient, she insists. It's about the lack of studies proving once and for all that vaccines don't cause autism, learning disabilities and a whole host of other maladies for certain kids.

"The question has always been, who are the vulnerable individuals who can't get through the process of vaccination without suffering a brain injury or immune system dysfunction or death?" she says.

But the anti-vaxxers have an evidence problem: The famous 1998 Wakefield study linking autism and the measles vaccine has been discredited, and there's little else showing any link with the condition.

Some cite a 2008 study suggesting a correlation between boys who were vaccinated and developmental disabilities, conducted by a graduate student and Melody Goodman, now an assistant professor at the Washington University School of Medicine.

But Goodman herself warns that the study has a few limitations: It's based on parents' self-attestation that their sons had disabilities, it doesn't find the same link for girls and it indicates correlation but not causation. "I do think there are some people who want to use it to say vaccination is bad, but that's not what we say in our study," Goodman says.

The vaccine injury program

Given the lack of research on their side, vaccine opponents have largely focused on questioning studies cited by medical experts — and arguing that there needs to be more research, period. Until you can definitively prove vaccines don't cause harm, they should be suspended or, at the very least, parents should be given ample opportunity to opt out, they say.

Demanding absolute proof that vaccines don't cause a whole host of conditions is an unfair demand on science, according to Sawyer. "That's a fundamental problem with science," he says. "It's very hard to prove a negative."

Another point often made by anti-vaxxers: The National Vaccine Injury Compensation Program. The program, established by Congress in 1988 to shield vaccine-makers from lawsuits, has awarded $2.8 billion for 3,941 claims of injury or death. Another 9,867 claims have been dismissed.

Vaccine advocates say that doesn't prove the 3,941 awarded people have been injured by or died from vaccines — it just means that judges were sufficiently convinced by their claims. But Sears says doctors are too dismissive of the awards.

"I don't think the vaccine injury court would pay out so much money for reactions that aren't really happening," Sears said.

But to many anti-vaxxers, the mere existence of the injury court proves the federal government has conspired to hide all the facts about vaccines while protecting drug companies who make bad products.

"I vaccinated my children, but what I did not understand is that the risks were understated," says Louise Kuo Habakus, a radio host and author of the book Vaccine Epidemic. "They told me, 'they're so safe, they're like water.' I was never told billions of dollars were paid out to people because of injury."

The CDC admits that vaccines can cause some serious side effects, although they're rare. The Tdap shot can cause seizures in one child out of 14,000. That ratio is one to 3,000 for the MMR vaccine. In extremely rare cases — less than one in a million — both shots can lead to long-term seizures, coma or permanent brain damage.

What anti-vaxxers dispute is how often those serious side effects occur.

"There is disagreement about how often it happens," Fisher says. "It's not just we believe, we know it happens more often than the government authorities are willing to admit."

Guggie Daly believes she was injured by vaccines as a kid and doesn't want the same to happen to her own children. Daly says she experienced seizures after getting the Tdap vaccine because she is genetically predisposed for bad reactions from certain medications.

Habakus says vaccines injured her children, which prompted her to look into the issue. She makes the point that many anti-vaxxers make, which is that many of the infectious diseases that children are vaccinated against, like measles, aren't usually fatal.

"I do believe more people would be more concerned about vaccines and less concerned about the disease if they did research and found out what is happening," Habakus says. "People die following vaccination. No one has died of measles in the past 10 years."

But no one has recently died of the measles in the U.S. because there haven't been enough cases, statistically speaking. Out of every 1,000 cases, one or two people are likely to die, experts say.

Still, for parents who either never themselves had measles or mumps, or made it through the diseases with relative ease, the thought that their child could experience a severe, albeit rare, reaction to a shot seems scarier than the diseases themselves.

"I had the measles before the vaccine came out. I was fine," Andrade says. "I had the mumps, I had the chicken pox. I had it all."